Search

In this brief, a novel distributed cascade robust feedback control approach is proposed for formation and reconfiguration control of a team of vertical takeoff and landing (VTOL) unmanned air vehicles (UAVs). This approach is based on dynamic communication network. It guarantees intervehicle collision avoidance and considers dynamic constraints of UAVs. In the outer loop of the cascade formation control, a potential field approach is used to generate a desired velocity for each UAV, which ensures that the team of UAVs can perform formation flying, formation rotating and reconfiguration, avoid intervehicle collision, as well as track a specified virtual leader. In the inner loop of the cascade formation control, the velocity of each UAV is designed to track its desired velocity generated by the outer loop, subject to dynamic constraints. The proposed approach is demonstrated via both simulation and flight test.

A set of algorithms are developed to estimate the air velocity of the quadrotors by fusing the plant model of the three-dimensional aerodynamic force and the IMU (inertial measurement unit) measurement. The main ideas are to compute out the air velocity of the quadrotors at first with the measured load acceleration and the model of the aerodynamic force, and then to smooth the computed results with the extended Kalman filtering against the model uncertainties. The developed algorithms are verified in the closed-loop flight control system. The simulation results demonstrate that the air velocity of the quadrotors are estimated well in the large airspeed and the resulting closed-loop system with the estimated air velocity can achieve almost the same flight performances as that with the real air velocity.

In this paper, a novel motion planning approach is proposed for high-speed flight of Micro Air Vehicles (MAVs) in unknown cluttered environment using a stereo camera as unique sensor. The proposed motion planning works directly on a depth map which represents partial surrounding environment due to limited field of view (FOV) of the stereo camera. The depth map updates at each sampling time. An optimal local target is selected from a set of local targets to which line-of-sight paths are collision-free. Then an optimal collision-free trajectory satisfying kinematic constraints is generated. The simulation results demonstrate the effectiveness of the proposed motion planning approach.

A hierarchical composite nonlinear feedback (HCNF) control technique is proposed in which the auxiliary integrators are introduced to remove the steady-state bias due to the disturbances. The main idea of HCNF is to separate the control design of the auxiliary integrators and the composite nonlinear feedback (CNF) control design. The auxiliary integrators are applied only to remove the steady-state bias by automatically adjusting the commands to be tracked by the CNF control law in which the CNF control design does not involve with the auxiliary integrators. The HCNF control technique is applied to design the attitude control law of a maneuvering flight control law for a quadrotor. The resulting closed-loop system is verified in simulation successfully to complete the maneuvering flight.

In this paper, a nonlinear flight control law is designed for a hybrid unmanned aerial vehicle (UAV) to achieve the advanced flight performances with the autonomous mission management (AMM). The hybrid UAV is capable of hovering like quadrotors and maneuvering as fixed-wing aircraft. The main idea is to design the flight control laws in modules. Those modules are organized online by the autonomous mission management. Such online organization will improve the UAV autonomy. One of the challenges is to execute the transition flight between the rotary-wing and fixed-wing modes. The resulting closed-loop system with the designed flight control law is verified in simulation and the simulation results demonstrate that the resulting closed-loop system can successfully complete the designated flight missions including the transition flight between the rotary-wing and fixed-wing modes.

A comprehensive model of a quadrotor is built for the maneuvering flight control design in which the nonlinearities of the quadrotor become dominant. The modeling is based on the components of the quadrotors such as the propellers by ignoring the weak coupling among the four propellers. The property of the propellers is tested in the wind tunnel in presence of the relative air flow and in each scheduled condition. The comprehensive model of the quadrotor is derived with the Newton's laws by integrating the property of the propellers. The built model is verified with the wind tunnel test data and The verification results show that the output of the propeller model is matched well with the test data. The built model is useful to the maneuvering flight control design of the quadrotors in high speed and large acceleration as the kinematical and aerodynamic nonlinearities are formulated in the model.

The nonlinear flight control design with the hierarchical dynamic inversion (HDI) and recursive control (RC) approaches is presented based on the comprehensive model of a quadrotor to implement the maneuvering flight in high speed and large acceleration. The flight control design comprises the kinematical control, command generation and dynamic control design. The command generation is to convert the required acceleration from the kinematical control into the flight commands of the roll, pitch angles and the heave load acceleration that the dynamic control laws can easily track. The designed nonlinear flight control laws are verified in simulation based on the comprehensive model of the quadrotor. The simulation results demonstrate that the resulting closed-loop system can successfully implement the maneuvering flight in high speed and large acceleration as well as its robustness against the model uncertainties is well. The introduction of the derivative commands of the roll and pitch angles yields a novel flight mode in which the quadrotor head points to a designated direction while the quadrotor conducts the maneuvering flight.

This paper studies vision-aided inertial navigation of small-scale unmanned aerial vehicles (UAVs) in GPS-denied environments. The objectives of the navigation system are to firstly online estimate and compensate the unknown inertial measurement biases, secondly provide drift-free velocity and attitude estimates which are crucial for UAV stabilization control, and thirdly give relatively accurate position estimation such that the UAV is able to perform at least a short-term navigation when the GPS signal is not available. For the vision system, we do not presume maps or landmarks of the environment. The vision system should be able to work robustly even given low-resolution images (e.g., 160 ×120 pixels) of near homogeneous visual features. To achieve these objectives, we propose a novel homography-based vision-aided navigation system that adopts four common sensors: a low-cost inertial measurement unit, a downward-looking monocular camera, a barometer, and a compass. The measurements of the sensors are fused by an extended Kalman filter. Based on both analytical and numerical observability analyses of the navigation system, we theoretically verify that the proposed navigation system is able to achieve the navigation objectives. We also show comprehensive simulation and real flight experimental results to verify the effectiveness and robustness of the proposed navigation system.

Majority of today's fixed-pitch, electric-power quadrotors have short flight endurance ($, Comment: 6 pages